Analysis of the dose-response relationship of histamine and N tau-methylhistamine.

The dose-response relationship of histamine (Hi) and N tau-methylhistamine (MeHi) was analysed in isolated ileum and the right auricle of the guinea pig, in isolated mouse stomach and in the blood flow through the submandibular gland of the cat. It was shown that the intrinsic activity of MeHi is slightly less than that of Hi. MeHi is equally active on either type of Hi receptor; the differences found in the isolated mouse stomach and in the blood flow through the salivary gland can be explained by non-equilibrium conditions. The dissociation constant of MeHi (3.5 X 10(-4) M) is nearly the same in the isolated ileum and the right auricle of the guinea pig and in isolated mouse stomach.